I had glow squid, slime and drowned spawn in a Trial chamber. Saw a bat too. There is no slime spawner in that Trial chamber and at that time no active zombie spawner.

Checked at least 2 Trial chambers and in both, mobs seem to spawn as they normally would do. Slime in slime chunks, Skeleton, zombie and spiders in light level 0, bats and glow squid as in caves